Ion exchange resins have been used in many areas for the recovery of valuble materials from aqueous solution. They are particularly suitable for processing dilute aqueous solutions frequently encountered in hydrometallurgy. Their insolubility eliminates the problem of contamination of the effluent stream and their chemical and mechanical stability reduces the economic loss of the active material. Also resins can be used with an unfiltered slurry of ore leach liquor where the difference in settling rate between the fine ore slurry particles and the larger, faster settling resin beads is a significant advantage. A further advantage is their utility with solutions too dilute for effective use of liquid-liquid extractants.
However, ion exchange resins are relatively nonselective for heavy metal ions, particularly at the acid pH of many ore leach liquors. Conventional cation exchange resins will absorb metal cations, and weak carboxylic acid resins are somewhat more selective than sulfonic acid resins. But both are relatively inactive at pH 1-4. Anion exchange resins, including the crosslinked vinylpyridine resins of D'Alelio U.S. Pat. No. 2,623,013 and the weak base ammonia epichlorohydrin resins of Anderson & Scheddel U.S. Pat. No. 3,340,208, also do not provide the selectivity necessary for many hydrometallurgical applications.
Greater selectivity is obtained with chelate exchange resins such as the resinous polymers of vinylaryl aminocarboxylic acids described by Morris U.S. Pat. No. 2,875,162. The use of these resins in recovery of copper, nickel, and cobalt from aqueous solutions is described in Mock, Calkins & Marshall U.S. Pat. No. 2,980,607 and Hampton & Mock U.S. Pat. No. 2,993,782. Melby U.S. Pat. No. 3,873,668 describes another copper selective resin containing 2,2'-bis(2"-pyridylmethylamino)biphenyl chelant ligands. Numerous other chelate exchange resins have been reported, for example, see Wheaton & Hatch in "Ion Exchange", J. H. Marinsky, ed., New York 1969, Vol. II, 221-2. But in spite of considerable effort, no chelate resins have yet demonstrated the requisite metal capacity, selectivity and cost performance essential for wide spread commercial use in such hydrometallurgical operations as the recovery of copper from acid leach liquors.
Stability constants have been reported by D. W. Gruenwedel, Inorg. Chem. 7, 495 (1968), for certain picolylamines as complexing agents for copper. H. A. Goodwin & F. Lions, JACS 82, 5013 (1960) describe several quadridentate chelate compounds containing picolylamine moieties. However, no mention is made of a polymer containing these moieties or of their chelate selectivity.